1. Field of the Invention
The present invention relates to a gate drive device for a display device and the display device having the same. More particularly, the present invention relates to a gate drive device improving charging time of sub pixels in a display device, and the display device having the gate drive device.
2. Description of the Related Art
Recently, flat display devices, for example, organic light emitting display (“OLED”), plasma display panel (“PDP”), and liquid crystal display (“LCD”) devices have been developing more rapidly than cathode ray tube (“CRT”) devices. Among the flat display devices, the widely-used LCD device includes an upper display substrate and a lower display substrate in which electric-field generating electrodes (e.g. a pixel electrode and a common electrode) are formed. Further, the LCD device includes switching elements, display signal lines, and a gate drive portion to generate gate control signals for turning the switching elements on and off. The gate drive portion includes a shift register receptive to outputting gate control signals to gate lines, a level shifter, and an output buffer. The shift register includes multiple stages that are connected one after another to each other. Each stage generates outputs of each gate line in sequence and the generated outputs are applied to the gate lines through the level shifter and the output buffer.
A vertically aligned mode of the LCD device, in which liquid crystal molecules are vertically arranged with respect to the upper and lower display substrates at a no voltage-applied status, has been better received as it has a larger contrast and provides a wider basic viewing angle than other types of LCD devices. Herein, the basic viewing angle indicates the viewing angle having a contrast ratio of 1 to 10 or a threshold angle of brightness inversion among gray levels.
In the vertically aligned mode of the LCD device, there are several methods for performing a wide viewing angle (e.g. methods of forming a partially-removed portion of the electric-field generating electrodes and forming a protrusion on the electric-field generating electrodes). Because of the partially-removed portion and the protrusion control orientation of the liquid crystal molecules, the viewing angle may widen by realigning the liquid crystal molecules in several directions using the partially-removed portion and the protrusion.
However, the vertically aligned mode of the LCD device has a disadvantage of deteriorating a side viewing property compared to a front viewing property (e.g. having a narrower viewing angle). For one example, a patterned vertically aligned mode of the LCD device provided with the partially-removed portion of the electric-field generating electrodes becomes brighter from a front view toward a side view. In other words, the brightness of high gray levels has substantially the same level, so there is a problem of showing bad quality of images.
To solve the problems above, after one pixel is divided into two sub-pixels and the two sub-pixels are capacitively coupled, a method of varying a transmittance of the LCD device, which includes applying a voltage to one sub-pixel, causing voltage-drop by means of capacitive coupling on other sub-pixel, and having different voltages on the sub-pixels, has been suggested. However, when a gate voltage is applied to the two sub-pixels, each stage of the gate drive portion described above generates a gate voltage every one horizontal time (i.e. one horizontal time indicates a time in which one row of pixels is processed). At this time, the two sub-pixels are simultaneously turned on, thus different voltages may not be applied to the two sub-pixels. Although the two sub-pixels of the LCD device, in which a gate drive portion is formed on both end edges of the LCD device, are separately driven, manufacturing costs still rise and the occupied area of the gate drive portion increases, thus the size of the LCD device is increased.